(a) Field of the Invention
The present invention relates to a light guiding plate, a backlight assembly having the light guiding plate and a display device having the backlight assembly, and more particularly to, a light guiding plate capable of performing polarization transformation and polarization extraction, a backlight assembly having the light guiding plate and a display device having the backlight assembly.
(b) Description of the Related Art
As semiconductor techniques are rapidly developed, the demand for lightweight, compact liquid crystal display (“LCD”) devices increases greatly. An LCD is thin, lightweight, and has low power consumption compared to a cathode ray tube (“CRT”). For these reasons, LCDs are used extensively in a variety of applications as a substitute for a conventional CRT. Recently, LCD devices have been used as display devices for many information processing devices, such as display monitors, portable computer displays, desktop computer displays, high definition (“HD”) imaging systems, and the like.
In the LCD device, alignment of liquid crystal molecules is generally changed by applying voltages to the liquid crystal (“LC”) molecules. The change in alignment of the LC molecules results in a change in optical characteristics of liquid crystal cells such as birefringence, optical rotation, dichromatism and light scattering. By using the change in optical characteristics of the liquid crystal cells, an image can be displayed on the LCD device. The LCD device is a non-emission type apparatus which displays information by using optical modulation of the liquid crystal cells.
The LCD device includes an LCD panel and two polarization plates, which are attached on both surfaces of the LCD panel to polarize light. The polarization plates pass only the light having a predetermined polarization direction. The polarization includes P and S polarization components. The P polarization component denotes polarization of which a direction is perpendicular to a formation direction of a lattice structure of a respective polarization plate, and the S polarization component denotes polarization of which a direction is parallel to the formation direction of a lattice structure of a respective polarization plate.
Since half of the entire light incident on the LCD panel is removed by the corresponding polarization plate, only the polarized light, which is oriented along a predetermined direction, can be used by the LCD panel. Accordingly, the entire light incident on the liquid crystal display panel cannot be used, so that light efficiency decreases greatly.
In order to solve the above problem, a technique for increasing the light efficiency by modifying optical sheets has been researched. Namely, the optical sheets are modified to transform the polarization so as to increase the light efficiency. However, a plurality of the optical sheets are assembled together, so that fine gaps are formed between the optical sheets. Therefore, there is a limitation to the polarization transformation. In particular, due to the fine gaps, the light is subject to birefringence, so that the polarization transformation is not easily performed. As a result, although the optical sheets having a function of the polarization transformation, the polarization transformation efficiency is not very large due to the fine gaps between the optical sheets.
In addition, it is still difficult to assemble a plurality of the thin optical sheets together. Therefore, manufacturing productivity of the LCD device decreases.